This invention relates to electrical connective means for a cathode ray tube and more particularly, to an improvement in the means for effecting an external electrical connection with the conductive coating disposed on the exterior surface of the funnel portion of the tube.
It is a conventional construction practice for cathode ray tubes employed in television and like applications, to have an electrical conductive coating, usually carbonaceous in nature, deposited on the interior surface of the funnel portion of the glass envelope. This coating, which covers a major portion of the funnel area, is normally of the same electrical potential as the final electrode of the electron gun assembly. Disposed upon the exterior surface of the funnel portion of the tube envelope, and covering a large area thereof, is another electrical conductive coating which is also usually composed of a carbonaceous material. This outer coating is conventionally connected to ground, since it is substantially superjacently related to the interiorly disposed coating, with the glass wall of the envelope therebetween, a capacitive effect is formed which is commonly utilized in the operational circuitry for filtering purposes. Thus, it is important that an adequate ground connection be made and maintained with the exterior coating on the envelope. An accepted practice to ground this outer coating, as employed in television and allied display equipment, has been to use a spring-like or resilient means oriented in a manner to press or exert contact pressure against the external coating; the spring member in turn being connected to ground circuitry in the chassis. Some adaptations of this type of contact means employ expensive and intricate harness arrangements. A disadvantage of the resilient contactor is evidenced in the spring becoming loose and thereby losing constant contact with the tube. A further disadvantage has been noted in the use of such resilient contact means wherein, through shipment and environmental vibration, the spring arrangement tends to shift causing an abrasion or rub-off of particles of the external coating thereby resulting in a poor or inadequate connection.
Another priorly utilized means for making ground contact with the outer coating of the tube, has been the use of a strip of conductive material, one end of which was bonded to the envelope in a manner to make contact with the exterior coating and whereof the free end of the strip formed a tab for connection with the ground circuitry. A disadvantage of this flexible connective means was evidenced in the loosening of the strip and an area of the associated coating upon flexure of the connector.